The present invention relates to silicon oxide layer depositing methods.
In prior art, a silicon oxide film has been fabricated by plasma enhanced CVD by means of a glow discharge system in which a chemical reaction between silan and nitrogen oxide goes on at a substrate temperature of 200.degree. to 400.degree. C.
However, in silicon oxide films natural oxides are not removed and hydrogen resides at 10 atom %, so that the films is provided only with poor heat resistance.
Further, in such a silicon oxide layer remains residual charges due to residual dangling bonds and clusters of silicon. And because of these charges, it can not used as a gate insulating layer for MOS' and other integrated circuits. According to the prior art, hydrogen and OH- remain in the silicon oxide thus formed.
For instance, in case of a channel region of an insulated gate FET, Si--H bonds are easily cut by charges which are attracted by concentrated electric field on the gate-to-semiconductor interface. Thence dangling bonds resulting from the disconnected bond immediately constitute interface levels and therefore the device is significantly degraded.
Therefore, it has been demanded to fabricate in practice silicon oxide layers from gaseous silicon oxide which tends not to produce dangling bonds of silicon.